1. Field of the Invention
The present invention relates to a heat-developable light-sensitive material, and more particularly relates to a heat-developable light-sensitive material containing an improved light-sensitive silver halide catalyst and having an improved image stability to light after heat development with less heat fog.
2. Description of the Prior Art
Since photographic processes employing silver halide provide better photographic properties such as sensitivity or gradation than those in electrophotographic processes and diazo photographic processes, they have been widely employed. However, in these processes, the light-sensitive silver halide has to be developed with a developing solution after imagewise exposure, followed by liquid processings, e.g., stopping fixing, washing or stabilizing, in order to protect the formed image from changing in color or fading under normal room illumination, or to protect the background (white portions) non-image areas from being blackened under normal room illumination. There are many problems with liquid processings, in that much time and labor are necessary for the processings, that the handling of the chemicals is dangerous to humans, that the processing rooms and the workers, bodies and clothes are stained, and that pollution problems occur when the waste processing solutions are disposed of. Therefore, a high speed photographic light-sensitive material employing a silver halide has been desired which can be processed by dry treatment and in which stable images and a stable background which is hardly changed in color under normal room illumination, can be obtained.
Various attempts to achieve such have been conducted. For example, German Patents Nos. 1,123,203 and 1,174,157 disclose that heat development of a silver halide emulsion is possible by adding a 3-pyrazolidone type developing agent, and German Patent No. 1,175,075 discloses that heat development can be promoted in the presence of a substance capable of generating water under heating in the above case. Further, German Patent 1,003,578 discloses that a fixing agent for silver halide can be used together with a silver halide. However, it has been impossible with these techniques for the silver halide remaining after the dry processing of the light-sensitive materials to be completely stabilized to light. That is, there is no disclosure in the above three German Patents of fixing the developed photographic materials using a dry processing, and it would be predicted in German Patent No. 1,003,578 that an undesired reaction between the developing agent and the fixing agent would occur on storage of the light-sensitive material. Therefore, it is difficult to practically carry out the process as disclosed in German Patent No. 1,003,578. Such has been confirmed experimentally.
Heat-developable light-sensitive materials which have been thus far used as light-sensitive materials for forming photographic images using a dry processing systems are heat-developable light-sensitive materials utilizing a composition containing a silver salt of an organic acid, a small amount of a light-sensitive silver halide and a reducing agent as essential components. In such a light-sensitive system, the silver halide remaining in the light-sensitive material undergoes a change in color due to light after development and is not stabilized to light, but substantially the same results as in stabilization can be obtained. That is, in the system, since a small amount of silver halide is used and a large amount of an organic silver salt which is hardly blackened by light and is white or a light color are used, even if the color of the silver halide is changed by light, the white or lightly colored background can be maintained and the color change of silver halide is not perceived by the human eye. The light-sensitive material is stable at normal temperature, and when it is heated, after imagewise exposure, to a temperature of 80.degree. C or higher, preferably 100.degree. C or higher, the oxidation-reduction reaction of the organic silver salt oxidizing agent and the reducing agent occurs due to the catalytic action of silver halide located near these materials to form silver, whereby the exposed portions of the light-sensitive layer are promptly blackened to form a contrast between the exposed portions and the unexposed portions (background).
The present invention relates to an improvement in the above-described heat developable light-sensitive material, and particularly, relates to a method for forming a light-sensitive silver halide which is included in the heat developable light-sensitive layer. As the methods of forming such the light-sensitive silver halide, a method for forming a light-sensitive silver halide by the reaction of an N-halo compound with an organic silver salt is known. The present invention relates to an improvement in this latter technique, in which a particular N-halo compound is employed as the N-halo compound, whereby heat fog can be reduced and the light-stability of light-sensitive materials after development can be improved.